Cutting-edge technology makes new 35W bridge a model for future

Filling up at a gas station across from the new 35W bridge, Kelly Thayer said she's looking forward to using it, she said traffic has been a mess since the collapse and it's made her job driving a van tough. Still, she said she can't help but wonder how safe the new bridge will be.

"I have reservations about driving over any of the bridges here, especially after that collapse," Thayer said. "And watching them work on it, I'm like, is that cement dry? I go over the 10th Avenue Bridge all the time and I've been watching it piece by piece. I think they've done a great job in getting it done soon, but in doing that have they compromised any safety?"

A worker installing expansion jointsMPR Photo/Jess Mador

Thayer said she's hoping the new bridge is safer but she'll still be nervous driving on it. She said since the old bridge collapsed, she's held her breath going over every bridge in town.

She is not alone. Less than 14 months after the collapse, many people are taking a second look at bridges they used to take for granted.

Standing on the new bridge, the Department of Transporation's Kevin Gutknecht said there is no reason to worry about the new 10-lane bridge.

"We want people to know this is a high quality product, that we worked very hard to make sure it's built to specifications," Gutknecht said. "It's a much better bridge than was here before. There are no gusset plates on this bridge."

Gusset plates are large steel sheets that connected the old bridge's beams. A National Transporation Safety Board investigation found that cracked and corroded gusset plates were a major factor in the bridge's failure.

Anti-icing systemMPR Photo/Jess Mador

The key to the new design is redundancy, that means it's designed to transfer load between different parts of the bridge. If one section fails, the others will pick up the slack and prevent a collapse. The span is anchored to giant concrete and steel columns. The columns are attached to shafts drilled deep into the bedrock below, and each pier rests on solid ground.

Gutknecht said the new bridge is much safer than the old one.

"It is a good piece of construction and you know what, I'm going to drive my family over this bridge," he said. "I'm going to drive on this bridge and everybody who has worked on this project will drive their families and use this bridge."

The $234 million bridge was built using round-the-clock construction, in less than half the usual time it takes to build a project of this size. With demolition of the old bridge, the total cost comes to more than $400 million. About three-quarters of that came from the federal government. The state paid for the majority of the rest.

Transportation officials said the people of Minnesota are getting more than their money's worth. The bridge is the first in the country to use LED lights, which last longer and use less energy. The new onramps are longer, to give drivers a better sight line as they approach and cut down on accidents. The bridge also has anti-icing technology to prevent the deck from freezing and it's light rail ready.

Engineer Linda Figg, who collaborated on the design, said the bridge is built to last more than 100 years and handle double the weight of the vehicles expected to travel on it.

"This is a modern concrete bridge for the future composed of high strength, high performance concrete with significant levels of redundancy," Figg said. "That means that many of the elements all do the same job and in that way you have a lot of extra strength that is built into the structure."

The monument gateway atop the new bridgeMPR Photo/Bill Alkofer

But it's the so-called Smart Bridge technology that really sets it apart. The new span is fitted with 323 sensors that will take regular readings on the bridge's condition. Each one will monitor things like deck movement, stress and temperature. The data will be collected and analyzed by a team from the University of Minnesota. MnDot officials said the information will make bridge inspection and maintenance much easier over the life of the bridge.

Minneapolis driver Buku Bakke said he's got no reservations at all about driving on the new bridge.

"I trust the science in it," he said. I don't drive much but I'll drive over it, for sure."

That's just the reaction officials were hoping for.

Gallery

The Interstate 35W bridge is nearing completion, just over a year after the original span collapsed on August 1, 2007.MPR Photo/Brandt WilliamsView full galleryGovernor Tim Pawlenty announces the opening of the new 35W bridge at a Monday morning press conference.MPR Photo/Bill Alkofer